Since locomotion is essential for metastasis of tumor cells, we are studying the biochemical nature of this process. Human melanoma and breast cancer cells produce in culture proteins (approximately 55 KDa) that stimulate motility in the producer cells - autocrine motility factors (AMF). These have been purified in procedures involving sequential gel filtration, hydrophobic interaction and ion exchange HPLC. Studies on the mechanism of action of AMF have identified a pertussis- sensitive G protein pathway as a requirement for motility and exclude the adenylate cyclase system from having a direct role in cell motility. Requirements for extracellular Ca++ and for lipoxygenase metabolites of arachidonic acid were suggested in studies with murine tumor cell lines. Investigations of early morphological events in tumor cell locomotion have indicated that pseudopod formation may be necessary for initiating motility. Pseudopod formation appears to be independent of attachment mechanisms. Pseudopodia are enriched in receptors for matrix components and cytoskeletal proteins, suggesting a sensory role for them in cell locomotion. In exploratory studies on clinical applications of cell motility, we have found that urine samples from patients with urinary tract cancers contain motility factors whose potency is well correlated with the aggressiveness of the tumors. There may well be a family of motility factors with a common active site. This point and the role of motility factors in metastasis would be clarified when we have achieved one of our principal objectives: cloning the gene for AMF.